Accelerated life testing device and method

ABSTRACT

An accelerated life testing device and method including an accelerated life testing method for a test piece within a test chamber, the method including: establishing a first atmosphere within the test chamber; changing the first atmosphere to a second atmosphere to form a deposition layer on the test piece; changing the second atmosphere to the first atmosphere to remove the deposition layer from the test piece; and repeating the changing the first atmosphere to the second atmosphere and the changing the second atmosphere to the first atmosphere to form an oxidation layer on the test piece.

RELATED APPLICATION

The present disclosure claims priority to and the benefit of U.S. patentapplication Ser. No. 14/086,750, filed on Nov. 21, 2013, the contents ofwhich are hereby incorporated by reference in their entirety.

TECHNICAL FIELD

The technical field of this disclosure is qualitative testing devicesand methods, particularly, accelerated life testing devices and methods.

BACKGROUND OF THE INVENTION

Highly Accelerated Life Testing (HALT) is a qualitative test method usedto accelerate and identify failures in products, such as medicaldevices. The products are tested to failure to find failure modes and toidentify the root causes of product and sub-system failures. Oncefailure modes and causes are identified, the product design can beimproved to prevent or reduce the identified failures. The improvedproduct design can then be retested to confirm that the identifiedfailures are reduced. The HALT process results in rugged designs andhigh reliability products.

The HALT process can apply any stimulus to a product under test that canaccelerate failure in the product, providing an indication of failureslikely to occur in the field. One stimulus is temperature stress, whichcan be used in electronics testing to identify failures due to marginalcomponents, poor timing margins, and poorly mounted heat sinks. Anotherstimulus is vibration, which can be used in mechanical and electronicstesting to identify failures due to poor solder joints, loose hardware,and contact and wear between adjacent parts. Other stimuli used toaccelerate failure can include general humidity, over-voltage, andover-current.

Unfortunately, present HALT processes are not able to provide a stimuluswhich accelerates oxidation in the product under test. Oxidation in thefield normally occurs over a number of years, so failures in products inthe field are too late to contribute to improved product design. Theinability to accelerate oxidation during HALT processes prevents productdesign improvements from determining how oxidation affects the functionof the device and identifying areas on which to focus design efforts.This, in turn, prevents achievement of highest product quality, productreliability, and patient safety.

It would be desirable to have an accelerated life testing device andmethod that would overcome the above disadvantages.

SUMMARY OF THE INVENTION

One aspect of the invention provides an accelerated life testing methodfor a test piece within a test chamber, the method including:establishing a first atmosphere within the test chamber; changing thefirst atmosphere to a second atmosphere to form a deposition layer onthe test piece; changing the second atmosphere to the first atmosphereto remove the deposition layer from the test piece; and repeating thechanging the first atmosphere to the second atmosphere and the changingthe second atmosphere to the first atmosphere to form an oxidation layeron the test piece.

Another aspect of the invention provides an accelerated life testingdevice for use on a test piece, the device including: a test chamber forcontaining the test piece; and an atmospheric controller operablyconnected to the test chamber, the atmospheric controller being operableto control temperature and humidity within the test chamber. Theatmospheric controller is operable to form an oxidation layer on thetest piece by: establishing a first atmosphere within the test chamber;changing the first atmosphere to a second atmosphere to form adeposition layer on the test piece; changing the second atmosphere tothe first atmosphere to remove the deposition layer from the test piece;and repeating the changing the first atmosphere to the second atmosphereand the changing the second atmosphere to the first atmosphere to formthe oxidation layer on the test piece.

The foregoing and other features and advantages of the invention willbecome further apparent from the following detailed description of thepresently preferred embodiments, read in conjunction with theaccompanying drawings. The detailed description and drawings are merelyillustrative of the invention, rather than limiting the scope of theinvention being defined by the appended claims and equivalents thereof.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic diagram of an accelerated life testing device madein accordance with the invention.

FIGS. 2A-2D are diagrammatic views of a test specimen undergoingaccelerated life testing in accordance with the invention.

FIG. 3 is photocopy of a photograph of a test specimen showing oxidationstructure from accelerated life testing in accordance with theinvention.

FIG. 4 is a flow chart of an accelerated life testing method inaccordance with the invention.

DETAILED DESCRIPTION

FIG. 1 is a schematic diagram of an accelerated life testing device madein accordance with the invention. Changing between a first atmosphereand a second atmosphere in the test chamber of the accelerated lifetesting device alternately forms and removes a deposition layer on thetest piece, causing the surprising and unexpected result that anoxidation layer forms on the test piece.

The accelerated life testing device 100 is for use on a test piece 102.The accelerated life testing device 100 includes a test chamber 110 forcontaining the test piece 102 and an atmospheric controller 120 operablyconnected to the test chamber 110. The atmospheric controller 120 isoperable to control temperature and humidity within the test chamber110. The atmospheric controller 120 is operable to form an oxidationlayer on the test piece 102 by establishing a first atmosphere withinthe test chamber 110; changing the first atmosphere to a secondatmosphere to form a deposition layer on the test piece 102; changingthe second atmosphere to the first atmosphere to remove the depositionlayer from the test piece 102; and repeating the changing the firstatmosphere to the second atmosphere and the changing the secondatmosphere to the first atmosphere to form the oxidation layer on thetest piece 102. The accelerated life testing device 100 can optionallyinclude a vibration table 130 to which the test piece 102 can be securedand vibrated for testing response to vibration. The accelerated lifetesting device 100 can also optionally include atmospheric sensors andcontrol systems to monitor and automatically control the atmosphericconditions within the test chamber 110.

The test piece 102 as defined herein can be any component or assembly ofcomponents to which a Highly Accelerated Life Testing (HALT) process isto be applied. In one embodiment, the test piece 102 can be a personalmedical device, such as an insulin pump, a continuous glucose monitor,or the like. Other exemplary personal medical devices which can be usedas a test piece 102 include pumps, cell pumps, heart-rate monitors, ECGmonitors, pulse oximeters, blood pressure monitors, respiration ratemonitors, skin temperature monitors, electroencephalography (EEG)monitors, activity level monitors, vital sign monitors, and the like.The surfaces of the test piece 102 on which the oxidation layer formscan be made of metal or any other material desired on which an oxidationlayer can form.

The test chamber 110 can be any suitable enclosure for establishing anatmosphere around the test piece 102. In one embodiment, the testchamber 110 can provide a closed atmosphere, i.e., the test chamber 110is sealed or substantially sealed from the outside environment so thatgases and/or materials from the outside environment are not exchangedwith test chamber 110. In another embodiment, the test chamber 110 canprovide an open atmosphere, i.e., gases and/or materials from theoutside environment are added to or removed from the test chamber 110.

The atmospheric controller 120 controls temperature and humidity withinthe test chamber 110, changing between a first atmosphere and a secondatmosphere in the test chamber 110 to alternately form and remove adeposition layer on the test piece 102. This causes an oxidation layerto form on the test piece 102. The atmospheric controller 120 can beused for temperature stress testing and/or oxidation layer formation.

In one embodiment, the atmospheric controller 120 includes a temperaturecontroller 122 and a humidity controller 124. The temperature controller122 and the humidity controller 124 can be located within the testchamber 110, can communicate between the outside environment and thetest chamber 110, or can be located within a loop through which airand/or other gases are withdrawn from and returned to the test chamber110.

The temperature controller 122 can increase or decrease the temperaturewithin the test chamber 110. Examples of temperature controllers includea liquid nitrogen source, a cold gas source, a hot gas source, arefrigeration coil, a heating element, and the like. The gas sources(liquid nitrogen source, cold gas source, hot gas source) introducegases from the outside environment into the test chamber 110. The sealedsources (refrigeration coil, heating element) do not introduce materialfrom the outside environment into the portion of the test chamber 110including the test piece 102.

The humidity controller 124 can increase or decrease the humidity withinthe test chamber 110. Examples of humidity controllers include a watermister, a water drop injector, a dehumidifier, a desiccant, and thelike. The humidity controller 124 can add moisture to or remove moisturefrom the atmosphere within the test chamber 110. The water sources(water mister, water drop injector) introduce water from the outsideenvironment into the test chamber 110. The water removers (dehumidifier,desiccant) can condense or absorb moisture from the atmosphere withinthe test chamber 110.

The accelerated life testing device 100 can also optionally include anatmospheric sensor 140 to sense atmospheric conditions within the testchamber 110. The atmospheric sensor 140 can optionally generate anatmospheric signal 150 in response to the sensed atmospheric conditions,and the atmospheric controller 120 is responsive to the atmosphericsignal 150 to control the atmospheric conditions within the test chamber110. In one example, the atmospheric sensor 140 is a temperature sensorto sense the temperature within the test chamber 110. The temperaturesensor can generate a temperature signal in response to the sensedtemperature, and the atmospheric controller can be responsive to thetemperature signal to control the temperature within the test chamber110. In another example, the atmospheric sensor 140 is a humidity sensorto sense the humidity within the test chamber 110. The humidity sensorcan generate a humidity signal in response to the sensed temperature,and the atmospheric controller can be responsive to the humidity signalto control the humidity within the test chamber 110. When theatmospheric controller 120 is responsive to the temperature signal andthe humidity signal, the temperature signal and the humidity signal canbe used separately or in combination to establish or change theatmospheric conditions within the test chamber 110.

The accelerated life testing device 100 can optionally include avibration table 130 to which the test piece 102 can be secured forvibration testing. Pneumatic or electrodynamic actuators 132 can be usedto move the vibration table 130 in the test chamber 110. Vibrationtesting can be applied simultaneously or sequentially with temperaturestress testing and/or oxidation layer formation applied by theatmospheric controller 120.

FIGS. 2A-2D are diagrammatic views of a test specimen undergoingaccelerated life testing in accordance with the invention. An oxidationlayer forms on the test piece from alternately forming and removing adeposition layer on the test piece.

Referring to FIG. 2A, a test piece 202 is located within a firstatmosphere 250 within a test chamber (not shown). In this example, thetest piece 202 at the start of the accelerated life testing method isbare, without any oxidation layer.

Referring to FIG. 2B, the first atmosphere is changed to a secondatmosphere 252 to form a deposition layer 204 on the test piece 202. Thearrows 210 illustrate the moisture coming from the second atmosphere 252to form the deposition layer 204. In one embodiment, the temperature ofthe test piece 202 is below the dew point of the second atmosphere 252and the deposition layer 204 is liquid water. In another embodiment, thetemperature of the test piece 202 is below the frost point of the secondatmosphere 252 and the deposition layer 204 is frost or ice.

Referring to FIG. 2C, the second atmosphere is changed to the firstatmosphere 250 to remove the deposition layer 204 from the test piece202. The arrows 212 illustrate the moisture leaving the deposition layer204 and entering the first atmosphere 250. In one embodiment, thedeposition layer 204 is liquid water, which evaporates into the secondatmosphere 252. In another embodiment, the deposition layer 204 is frostor ice, which melts into liquid water and runs off the test piece. Inyet another embodiment, the deposition layer 204 is frost or ice, whichmelts into liquid water and evaporates into the second atmosphere 252(dual phase removal). In yet another embodiment, the deposition layer204 is frost or ice, which sublimates directly into the secondatmosphere 252 (single phase removal). Those skilled in the art willappreciate that in another embodiment, the second atmosphere can bechanged to another atmosphere different than the first atmosphere toremove the deposition layer 204.

Referring to FIG. 2D, the deposition layer on the test piece has beenalternately formed and removed a number of times by repeatedly changingbetween the first atmosphere and the second atmosphere, so that anoxidation layer 206 has formed on the test piece 202. The oxidationlayer 206 introduces an additional failure mode when used in HighlyAccelerated Life Testing (HALT). In one example, the oxidation layer 206forms after the deposition layer on the test piece has been formed andremoved approximately 10 times. In another example, the oxidation layer206 forms after the deposition layer on the test piece has been formedand removed over several hours. In one experimental example asillustrated in FIG. 3, the oxidation layer 206 of copper oxide wasformed on a printed circuit board made of FR4 fiberglass reinforcedepoxy laminate: the oxidation layer was bluish white and non-conductive,and had a thickness between 0.1 and 35 micrometers.

FIG. 3 is photocopy of a photograph of a test specimen showing oxidationstructure from accelerated life testing in accordance with theinvention. In this example, the test piece is a printed circuit board302 with an oxidation layer 306. The formation of the oxidation layer306 on the circuit board 302 was a surprising and unexpected result. Theoxidation layer 306 was formed by alternately placing the circuit board302 in a first atmosphere at 70 degrees Centigrade and 0 percenthumidity and a second atmosphere at −35 degrees Centigrade. Theatmosphere was changed from the first atmosphere to the secondatmosphere by admitting liquid nitrogen containing moisture into thetest chamber. The atmosphere was changed from the second atmosphere tothe first atmosphere by heating the inside of the test chamber with anelectrically powered resistive heating element. The oxidation layer 306formed after the deposition layer on the test piece had been formed andremoved 10 times over several hours. The oxidation layer 306 was foundto be made of copper oxide and have a thickness between 0.1 and 35micrometers. As illustrated in FIG. 3, the oxidation area extendedbeyond the surface of the copper on the circuit board and extended ontothe circuit board and nearby components.

FIG. 4 is a flow chart of an accelerated life testing method inaccordance with the invention. The accelerated life testing method 400for a test piece within a test chamber includes: establishing a firstatmosphere 410 within the test chamber; changing the first atmosphere toa second atmosphere to form a deposition layer 420 on the test piece;changing the second atmosphere to the first atmosphere to remove thedeposition layer 430 from the test piece; and repeating the changing thefirst atmosphere to the second atmosphere and the changing the secondatmosphere to the first atmosphere to form an oxidation layer 440 on thetest piece. The method 400 can optionally include vibrating the testpiece.

The establishing a first atmosphere 410 within the test chamber includesestablishing an atmosphere at a desired temperature and/or humidity. Inone example, the first atmosphere is established at 100 degreesCentigrade and 0 percent humidity. In other examples, the temperaturefor the first atmosphere is in the range of 65 to 100 degrees Centigradeand in the range of 0 to 10 percent humidity.

The changing the first atmosphere to a second atmosphere to form adeposition layer 420 on the test piece can include decreasing thetemperature within the test chamber, increasing the humidity within thetest chamber, or a combination of decreasing the temperature within thetest chamber and increasing the humidity within the test chamber. Thiscan form a deposition layer of liquid water, frost, or ice. In oneexample, the second atmosphere is established at 50 degrees Centigrade.In other examples, the temperature for the second atmosphere is in therange of −30 to −60 degrees Centigrade. Those skilled in the art willappreciate that the conditions of the first atmosphere and the secondatmosphere can be selected as desired for a particular application asrequired to form and remove the deposition layer.

The changing the second atmosphere to the first atmosphere to remove thedeposition layer 430 from the test piece can include increasing thetemperature within the test chamber, decreasing the humidity within thetest chamber, or a combination of increasing the temperature within thetest chamber and decreasing the humidity within the test chamber. Thedeposition layer can be liquid water, frost, or ice. When the depositionlayer is liquid water, the deposition layer can evaporate. When thedeposition layer is frost or ice, the deposition layer can sublimate, ormelt to liquid water then evaporate from or run off of the test piece.Those skilled in the art will appreciate that the deposition layer canbe partially or fully removed as desired for a particular application,i.e., a portion of the deposition layer can be left on the test pieceand the next deposition layer formed on top of that portion of thedeposition layer.

The repeating the changing the first atmosphere to the second atmosphereand the changing the second atmosphere to the first atmosphere to forman oxidation layer 440 on the test piece can be performed as many timesor for as long as desired for a particular application. In one example,the oxidation layer forms after the deposition layer on the test piecehas been formed and removed 10 times. In another example, the oxidationlayer 206 forms after the deposition layer on the test piece has beenformed and removed over several hours. In yet another example, therepeating continues for a predetermined number of 15 times, for apredetermined time of a few days, or until the test piece fails.

The method 400 can also include sensing an atmospheric condition withinthe test chamber, such as temperature, humidity, or a combination oftemperature and humidity. The method 400 can also include controllingthe atmospheric condition within the test chamber based on the sensedatmospheric condition.

The method 400 can optionally include vibrating the test piece.Exemplary vibrations can have a frequency of 6 to 10,000 cycles persecond within acceleration parameters 5 to 80 gRMS with random vibrationenergy density profiles, as desired for a particular application.

It is important to note that FIGS. 1-4 illustrate specific applicationsand embodiments of the invention, and are not intended to limit thescope of the present disclosure or claims to that which is presentedtherein. Upon reading the specification and reviewing the drawingshereof, it will become immediately obvious to those skilled in the artthat myriad other embodiments of the invention are possible, and thatsuch embodiments are contemplated and fall within the scope of thepresently claimed invention.

While the embodiments of the invention disclosed herein are presentlyconsidered to be preferred, various changes and modifications can bemade without departing from the spirit and scope of the invention. Thescope of the invention is indicated in the appended claims, and allchanges that come within the meaning and range of equivalents areintended to be embraced therein.

1. A qualitative testing device comprising: an enclosure suitable forestablishing an atmosphere around a test piece; and an atmosphericcontroller operatively connected to the enclosure, the atmosphericcontroller operable to repeatedly change between atmospheres in theenclosure to alternately form and remove a deposition layer on the testpiece, causing an oxidation layer to form on the test piece.
 2. Thequalitative testing device of claim 1, wherein the atmosphericcontroller further comprises at least one sensor and at least onecontrol system that monitors and controls atmospheric conditions withinthe enclosure.
 3. The qualitative testing device of claim 1, wherein theatmospheric controller further comprises a temperature controlleroperable to control temperature within the enclosure, and a humiditycontroller operable to control humidity within the enclosure.
 4. Thequalitative testing device of claim 3, wherein the temperaturecontroller and the humidity controller are located within the enclosureor within a loop through which air or other gases are withdrawn from andreturned to the enclosure.
 5. The qualitative testing device of claim 1,wherein the test piece comprises at least one metal surface on which theoxidation layer forms.
 6. The qualitative testing device of claim 1,wherein the enclosure further comprises a test chamber that provides aclosed atmosphere that is substantially sealed from an outsideenvironment.
 7. The qualitative testing device of claim 1, wherein theenclosure further comprises a test chamber that provides an openatmosphere.
 8. The qualitative testing device of claim 1, wherein thetest piece further comprises a circuit board.
 9. The qualitative testingdevice of claim 1, wherein the oxidation layer further comprises copperoxide.
 10. A qualitative testing method comprising: alternately formingand removing a deposition layer on a test piece located in an enclosureby repeatedly changing an atmosphere within the enclosure; and formingan oxidation layer on the test piece as a result of the alternatelyforming and removing the deposition layer.
 11. The method of claim 10,wherein the removing the deposition layer further comprises partiallyremoving the deposition layer, wherein a portion of the deposition layeris left on the test piece; and forming a next deposition layer on top ofthe portion that is left.
 12. The method of claim 10, wherein therepeatedly changing the atmosphere further comprises changing from afirst atmosphere to a second atmosphere and changing from the secondatmosphere to another atmosphere, wherein the another atmosphere issimilar or different than the first atmosphere.
 13. The method of claim10, further comprising sensing an atmospheric condition within theenclosure.
 14. The method of claim 13, wherein the sensing theatmospheric condition further comprises sensing temperature, humidity,or a combination thereof.
 15. The method of claim 13, further comprisingcontrolling the atmospheric condition within the enclosure based on thesensing the atmospheric condition.
 16. A method of accelerated lifetesting, the method comprising: forming a deposition layer on a testpiece by changing a first atmosphere to a second atmosphere within atest chamber containing the test piece; removing the deposition layerfrom the test piece by changing the second atmosphere to anotheratmosphere; alternately forming and removing the deposition layer on thetest piece by repeatedly changing between atmospheres; and forming anoxidation layer on the test piece from the alternately forming andremoving the deposition layer on the test piece.
 17. The method of claim16, wherein the changing the first atmosphere to the second atmospherefurther comprises setting a temperature of the test piece below a dewpoint of the second atmosphere, wherein the deposition layer is liquidwater.
 18. The method of claim 16, wherein the changing the firstatmosphere to the second atmosphere further comprises setting atemperature of the test piece below a frost point of the secondatmosphere, wherein the deposition layer is frost or ice.
 19. The methodof claim 16, wherein the changing the second atmosphere to anotheratmosphere further comprises changing the second atmosphere to the firstatmosphere or to an atmosphere different than the first atmosphere. 20.The method of claim 16, wherein the forming the oxidation layer furthercomprises alternately forming and removing the deposition layer on thetest piece for a predetermined number of times or for a predeterminedduration.